Many of the liquid crystal display apparatuses that display a color image include a color filter that allows light rays of red (R), green (G), and blue (B) to pass through respectively three sub pixels into which one pixel is divided. Since about two-thirds of backlight rays irradiating a liquid crystal panel are absorbed by the color filter, a color-filter liquid crystal display apparatus has a problem of low light use efficiency. For this reason, a field-sequential liquid display apparatus that displays a color image without using the color filter gains attention.
In accordance with the field sequential technique, a display period (1 frame period) of one screen is divided into three subframe periods. The subframe period is also referred to as a subfield period. In the discussion that follows, the term subframe period is used consistently. During a first subframe period, a red screen is displayed in response to a red component of an input signal. During a second subframe period, a green screen is displayed in response to a green component of the input signal. During a third subframe period, a blue screen is displayed in response to a blue component of the input signal. As described above, colors are displayed one by one so that a color image is displayed on a liquid crystal panel. The field-sequential liquid crystal display apparatus is free from the color filter, and provides a light use efficiency about 3 times as high as that of the color-filter liquid crystal display apparatus.
However, the field sequential color technique suffers from a problem of a generation of color break. FIG. 27 illustrates the generation principle of the color breaking. In a section A of FIG. 27, the ordinate represents time, and the abscissa represents location on a screen. When an object moves within a display screen, a line of sight of a viewer typically keeps track of the object and moves in a movement direction of the object. For example, when a white object moves from left to right within the screen display as illustrated in FIG. 27, the line of sight of the viewer moves in a slant arrow-headed line direction. If the three subframe images of R, G, and B are extracted from a video at the same instant, the objects in the subframe images are at the same location. For this reason, a color break takes place in the video focused on the retina as illustrated in a section B of FIG. 27.
Japanese Patent No. 3766274 describes as below how the color break is reduced in a color display apparatus such as a liquid crystal display apparatus. In the color display apparatus, one frame period includes at least 4 or more subframes. The first through third subframes respectively display red, green, and blue. The fourth subframe displays a color presentation of non-3-primary colors, i.e., a presentation of at least two colors (a color mixed display). A color displayed by the fourth subframe is determined by performing a specific statistic process on an original image signal including an RGB signal of one frame.
The following related art in the field of the present invention is also known. According to Japanese Unexamined Patent Application Publication No. 9-90916, one frame period includes three subframes of the 3-primary colors of red, green, and blue, and a subframe of white or of an intermediate color between the three-primary colors. According to Japanese Patent No. 3215913, one frame period is divided into four subframes, and a fourth subframe presents a white display. According to Japanese Patent No. 3952362, one frame period is divided into four subframes, and the color of a light source that lights on in a fourth subframe is determined based on the mean value of luminance of the colors. According to Japanese Unexamined Patent Application Publication No. 2003-241165, RGB driving and RGBW driving is switchable so that the RGB driving is performed in a bright environment, and the RGBW driving is performed in a dark environment in order to prevent color breaking.